INSPEC06164

• Permit No: M1994117
• IBM Index Class Name: Inspection
• Doc Name: MINERALS PROGRAM INSPECTION REPORT
• Inspection Date: 10/7/1998
• Media Type: D
• Archive: No

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MINE ID # O,R PROSPECTING ID # M-94-117
INSPECTION DATE 10/7/98 INSPECTOR'S INITIALS ACS
OBSERVATIONS
This inspection was conducted to evaluate the status of the tailings pond expansion approved
in technical revision TR-03. Tom Marano representing the Operator (ITEC) was present during
the :inspection, and Larry Owen and John Friedman with the design and quality assurance
engineering firm on the project (McCulley, Frick and Gillman) were also present. The
construction of the upstream/centerline dam raise has been completed, and the pond expansion
area has been lined. The approved plan calls for the wedge of tailing located in the area
between the new embankment and the interim berm to be removed and placed in the new lined
pond expansion area. Following removal of this wedge of tailing, the raised embankment and
the tailing removal area is to be lined.
At the time of this inspection, the Operator was using a hydraulic excavator working from the
dam crest and equipped with a toothless bucket to scalp the organic material (cattails) from
the surface of the old tailing. The Operator is concerned that removal of the wedge of
tailing in accordance with the approved plan may destabilize the upstream embankment raise.
To evaluate this concern, the design engineer conducted a stability analyses for a failure
surface coincident with the tailing/HOPE liner interface. Using an assumed value, based on
typical values from the literature, for the resistance to interfacial shear, it was
determined that the tailing/liner interface is probably the critical failure surface, and
that based on the assumed shear resistance values, the safety factor was less than unity.
Removal of the wedge of tailing in accordance with the approved plan would shorten the length
of the critical failure surface and would eliminate the resistance to failure that the weight
of the tailing provides, thus lowering what may already be a marginal safety factor.
The Operator proposed a plan whereby the wedge of tailing would remain in-place, with only
the surficial organic material removed. The surface of the tailing would then be stabilized
by placement .of a biaxial geogrid and a thin layer of granular soil, and the new GCL/HOPE
linear system would be installed. To evaluate the Operator's proposal, the tailing surface
was inspected. The slimes ponds, where the cattails were growing, consist of rock flour
(cleay sized particles with no cohesion) with some silt; this material is saturated and soft
and can be expected to be more compressible than the sandy tailings tested to estimate
con:;olidation under the upstream dam raise (see TR-03). The exposed tailings surface between
the two slimes ponds is desiccated at the surface and interlaced with deep mud cracks, but
can be assumed to be saturated below the surface.
It :is the Division's position, in accordance with accepted protocols for liner installations,
that these soft, saturated, presumably under-consolidated tails are not a suitable foundation
for the new liner system, even with the installation of a geogrid. However, the Division
shares the Operator's concern that removal of the wedge of tailing in accordance with the
approved plan may destabilize the raised embankment. The Division is also concerned that the
upstream embankment raise, which was approved in the technical revision TR-03 with an end-of-
construction safety factor of 1.2, may have a safety factor at this time at or just slightly
above unity.
In order to address the Division's concerns, and to allow the Operator to complete the
construction of the tailings pond facility and put it into service, the following design
modifications were discussed:
1. Scalp organics from surface of tails.
2. Install biaxial geogrid over tailing surface